1. Field of the Invention
The present invention relates to a process for preparing a biologically active system comprising biological cells and a solid support therefor, to a system so prepared and to the use of such a system.
In this specification, we use the term "biological cell" broadly, to include for example bacteria, fungi, spores derived therefrom and cells derived from multicellular organisms.
2. Description of the Prior Art
Biologically active systems are known in which a biological organism and/or an active material derived from a biological organism acts as a means by which a chemical reaction, usually a relatively specific reaction, is promoted or performed. Such an organism may be known as a biocatalyst. Such a biological organism or its derivative is thus an integral part of the reaction. Usually moreover the biological material has been especially selected for the particular role it has to play. Its selection and any subsequent purification can be costly and time consuming. The biological material can thus be expensive and valuable. It can therefore be important that it is both used efficiently during any reaction and is not inadvertently lost during or after the reaction.
Supports for enzymes are well known.
U.S. Pat. No. 4,629,742 describes a biologically active system in which a lipase enzyme is immobilised by adsorption on a microporous synthetic thermoplastic hydrophobic polymer. The polymer has a cellular structure, with voids (cells) interconnected by holes, and is typically the material sold under the trade mark Accurel (of Enka, The Netherlands). Accurel is made by cooling a solution of the polymer. The immobilized lipase is used for hydrolysis of liquid fats. The same kind of porous polymer is used in the process of U.S. Pat. No. 4,539,294, in which proteins, e.g. enzymes, are immobilized after first soaking the support with a dilute long-chain cationic solution.
U.S. Pat. No. 4,551,482 also discloses immobilization of an enzyme on a support. In this case the support is hydrophilic macroporous beads. Polystyrene is sulphonated and then charged with polyethyleneimine. The enzyme is said to be ionically bound to the carrier. The support may be formed by suspension polymerization of, for example, styrene and divinylbenzene, with water as the external (continuous) phase. A pore-forming agent. e.g. alkanes, are used to produce the porosity. Alternatively block polymerization is employed, followed by comminution.
An example of chemical bonding of an enzyme to a carrier is to be found in EP-A-147914, where the carrier is controlled pore glass or paper.
It is well known to trap cells within polymer gels. These are formed with the cells present.
The immobilization of biological cells on preformed solid porous support materials appears to be less well-described. In a review in Chemical Engineering Science Vol. 40, No. 8, pp 1321-1354, 1985, Karel et. al. described entrapment of cells in preformed porous matrices. The examples of matrices given are all inorganic.
Use of a porous polyurethane foam, with a large pore size of 2.54 mm, for entrapment of a fungus is described in for example Enzyme Microb. Technol. 1987, vol. 9, December by Turker and Mavituna. WO 87/02704 describes a process wherein the cells are held in cavities between microparticles which are bonded at points of contact to construct a rigid matrix, after the cells have been mixed with the particles. The cells are thus mechanically trapped in the voids of the matrix.